Having been first introduced in the early twentieth century, the Fischer-Tropsch reaction for catalytically converting carbon monoxide and hydrogen into hydrocarbons is very well known. Furthermore, numerous improvements to the process, including the development of more efficient and selective catalysts, have been made. All currently known Fischer-Tropsch processes, however, produce a synthetic crude, “syncrude,” which contains primarily paraffins, and olefins with varying amounts of oxygenates. The oxygenates typically include primary and internal alcohols, the major portion, aldehydes, ketones and acids. The heavy portion of syncrude must be hydroprocessed into usable products. The presence of oxygenates presents certain problems with processing the syncrude, including a negative impact on hydroprocessing catalysts and necessitating an increase in the severity of hydroprocessing. The oxygenate content is generally higher in the lower boiling range distillation cuts of the Fischer-Tropsch product and declines precipitously at the 600° F. cut point. One method of avoiding the negative impact of the oxygenates on the hydroprocessing catalysts is to bypass the lower boiling range distillation cuts around the hydroprocessing unit. The lower boiling range distillation cuts, including any oxygenate content, are then used to reblend the lower boiling range cut with the hydrocracked higher boiling range distillation cut to form the product fuel. While a bypassed 250-400° F. distillation cut has no appreciable negative impact when re-blended into the product fuel, reincorporation of a bypassed 400° F.+ distillation cut impairs the low temperature properties of the product fuel. Therefore, it is common to hydroprocess the entire 400° F.+ fractions, including hydrogenation of oxygenates, which has significant impact on catalyst life and causes yield loss. Catalytic hydroprocessing catalysts of noble metals are well known, some of which are described in U.S. Pat. Nos. 3,852,207; 4,157,294; 3,904,513. Hydroprocessing schemes utilizing non-noble metals, such as cobalt catalysts, promoted with rhenium, zirconium, hafnium, cerium or uranium, to form a mixture of paraffins and olefins have also been used. Such hydrotreatment, however, is expensive, utilizing high cost catalysts, which are degraded by the presence of alcohol thereby necessitating frequent replenishment.
There remains a need, therefore, for an improved integrated Fischer-Tropsch process in which the alcohol content of the oxygenates produced in the Fischer-Tropsch reaction may be wholly or partially removed at a lower cost and without a significant loss of yield.